The Sims 3. CAN it run smoothly?

This is not as much about setups as it is about the game itself, so I post here. I'm baffled about this game really...made by such a big company, HUGE amount of content, and yet all I see are people having problems, having to find fixes, needing to download mods just to stop the game from crashing from how it has been coded (cars building up for example, or dead Sims).

I have upgraded my setup, and while the game loads fast and I have none of the annoying lag I used to get, the game still feels...unstable. Sims sometimes stutter when they walk, other times they do not. Rendering can be smooth as butter sometimes and then suddenly spike and look very weird.

I'm about to give up, IS it possible to play this game without constantly having to think about it having issues just to run?

My collection of mounts
WoW without flying is like having a pizza you know that you enjoy but then have someone treating you like a moron and telling you that "No, you won't enjoy THESE particular toppings for reasons WE made up". And some people are dumb enough to accept being told what to like.

I bought for my sister ( as in bought the game from Origin store - legit ) with many more addons and DLCs and such. She had no issues at all.
She complained only with an DLC not working, which we got sorted in 10 mins. What OS you have? Maybe that's the problem or a part of the problem.

At best, try google to solve all your problems.

EDIT: Also, my comp specs are not great, and it still runs smooth. I'll ask her and I'll contribute more if she says something is weird.